No one ever HAS to file form 2555. You CHOOSE to file form 2555 in order to take advantage of the tax benefit provided by being able to exclude the income earned from US tax.

What I have done in this situation, (where a taxpayers will meet the physical presence test, but has not yet by the filing due date) is to extend the return, until after they have actually met the test, so that I can properly complete the necessary travel date information on the 2555.